Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!selfless.tophat.at!newsfeed.xs4all.nl!newsfeed5.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'ok.': 0.04; 'subject:Does': 0.04; 'memory.': 0.05; 'chunk': 0.07; 'mode,': 0.07; 'data:': 0.09; 'underlying': 0.09; 'output': 0.11; 'subject:file': 0.13; 'wrote:': 0.15; 'allocate': 0.16; 'dma': 0.16; 'file.close()': 0.16; 'file.read()': 0.16; 'from:addr:awilliam': 0.16; 'from:addr:whitemice.org': 0.16; 'from:name:adam tauno williams': 0.16; 'hashlib': 0.16; 'message- id:@linux-yu4c.site': 0.16; 'operations?': 0.16; 'received:72.14.190': 0.16; 'received:72.14.190.87': 0.16; 'received:mail.wmmi.net': 0.16; 'received:wmmi.net': 0.16; 'reply- to:addr:awilliam': 0.16; 'reply-to:addr:whitemice.org': 0.16; 'def': 0.16; 'digest': 0.19; 'header:In-Reply-To:1': 0.22; 'tue,': 0.23; 'string': 0.26; 'function': 0.26; 'received:72.14': 0.26; 'import': 0.29; 'example': 0.30; 'i/o': 0.30; 'subject:support': 0.30; 'subject:?': 0.31; 'does': 0.32; 'break': 0.33; 'to:addr :python-list': 0.34; 'rule': 0.34; 'skip:o 20': 0.36; 'file': 0.36; 'streaming': 0.37; 'some': 0.37; 'could': 0.37; 'subject:: ': 0.38; 'something': 0.38; 'header:Mime-Version:1': 0.39; 'data': 0.39; 'to:addr:python.org': 0.39; 'your': 0.60; 'matter': 0.61; 'header:Reply-To:1': 0.71; 'reply-to:no real name:2**0': 0.72; 'stream': 0.77; 'blocks.': 0.84; 'filesystem.': 0.84; 'streams': 0.84; 'subject:mode': 0.84; 'movies': 0.93 Subject: Re: Does hashlib support a file mode? From: Adam Tauno Williams To: python-list@python.org Date: Wed, 06 Jul 2011 06:55:31 -0400 In-Reply-To: <952b0e40-3308-4dbc-b107-8fbe96014199@e17g2000prj.googlegroups.com> References: <952b0e40-3308-4dbc-b107-8fbe96014199@e17g2000prj.googlegroups.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.0.2 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list Reply-To: awilliam@whitemice.org List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 38 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1309951505 news.xs4all.nl 21790 [2001:888:2000:d::a6]:34050 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:8927 On Tue, 2011-07-05 at 22:54 -0700, Phlip wrote: > Pythonistas > Consider this hashing code: > import hashlib > file = open(path) > m = hashlib.md5() > m.update(file.read()) > digest = m.hexdigest() > file.close() > If the file were huge, the file.read() would allocate a big string and > thrash memory. (Yes, in 2011 that's still a problem, because these > files could be movies and whatnot.) Yes, the simple rule is do not *ever* file.read(). No matter what the year this will never be OK. Always chunk reading a file into reasonable I/O blocks. For example I use this function to copy a stream and return a SHA512 and the output streams size: def write(self, in_handle, out_handle): m = hashlib.sha512() data = in_handle.read(4096) while True: if not data: break m.update(data) out_handle.write(data) data = in_handle.read(4096) out_handle.flush() return (m.hexdigest(), in_handle.tell()) > Does hashlib have a file-ready mode, to hide the streaming inside some > clever DMA operations? Chunk it to something close to the block size of your underlying filesystem.